The present invention relates in general to wireless communications, and in particular to canceling spurious signal content from signals to be transmitted.
Wireless communication systems often incorporate predistortion techniques configured to pre-process signals for transmission to compensate for non-linearities or like anomalies inherent to transmission. Unfortunately, the compactness of wireless architectures makes these systems prone to having spurious noise injected into the signals to be transmitted. The source of the spurious noise may take many forms, including the various local oscillators facilitating reception and transmission of wireless communication signals, harmonics and mixing products from mixing circuitry, and the like. Unfortunately, compensating for the unwanted injection of spurious noise content is difficult to address, and can be even more difficult to address in a cost-effective manner in systems incorporating predistortion techniques.
Accordingly, there is a need for a technique to cancel spurious noise in wireless communication systems, and a further need for a technique to cancel spurious noise in wireless communication systems incorporating predistortion techniques to compensate for non-linearities or other anomalies in the transmission path.
The present invention provides a technique for canceling spurious noise content in transmitted signals. During transmission, the transmitted signals are fed back to predistortion and cancellation circuitry adapted to provide a predistortion component for signals to be transmitted, as well as to compensate for spurious noise injected into the system. In a first path, the predistortion and cancellation circuitry will predistort the baseband signals to compensate for non-linearity and like anomalies injected by the transmission circuitry to provide a predistorted output. Along a second path, a fast Fourier transform is performed on the feedback signal. The resultant frequency domain signal is then processed to detect spurious noise content above a defined threshold, throughout the range or within defined bands. The spurious noise content is identified and used to recreate a replica of the noise content. The replica will preferably have the same phase and frequency, and a magnitude sufficient to reduce or eliminate the content to a desired degree. The replicated signal is then negatively added to the predistorted signals to create a final signal for transmission.
Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures.